Funding for this research was provided by:
National Natural Science Foundation of China (82041020, 71901067)
Received: 13 August 2020
Accepted: 9 November 2020
First Online: 9 December 2020
Ethics approval and consent to participate
: The study and Liu (2018, 2019) [CitationRef removed, CitationRef removed] were supported by the Natural Science Foundation of China (91546203, 71771213). This study uses only publicly available data and does not involve any physical, social or legal risks to the users, whose personal identifying information are either unknown to the public or removed if they choose to post online.
: Not applicable.
: The authors declare that they have no competing interests.